1. Field of the Invention
The present invention relates to a liquid delivery device for delivering a special chemical solution such as a resist solution, a wafer protection solution, or the like which will be used in the fabrication of semiconductor devices, a method of controlling such a liquid delivery device, and a liquid delivery pump for delivering such a special chemical solution.
2. Description of the Prior Art
one generally known liquid delivery device for delivering a special chemical solution comprises a positive-displacement piston pump disposed in a liquid delivery line which interconnects a liquid supply and a liquid consumption site, for delivering the chemical solution under a predetermined pressure.
The liquid delivery device has a inlet valve placed in an inlet pipe of the liquid delivery line which is connected to an inlet port of the positive-displacement piston pump, and an outlet valve disposed in an outlet pipe of the liquid delivery line which is connected to an outlet port of the positive-displacement piston pump, the inlet and outlet valves being used to prevent the chemical solution from flowing back into the positive-displacement piston pump. The liquid delivery device needs to have a flow regulating valve for regulating the flow rate of the chemical solution.
Another liquid delivery device which is widely used in the art is an in-line pump comprising an integral assembly of a pump and a motor for easy installation in a liquid delivery line. The in-line pump has a main shaft rotatable with an impeller by the motor, the main shaft being rotatably supported by rolling bearings and slide bearings.
The positive-displacement piston pump has been disadvantageous in that the piping system is structurally complex because of the valves that are positioned in the liquid delivery line. If the chemical solution to be delivered contains a solvent, then when the positive-displacement piston pump is shut off after a certain amount of the chemical solution has been delivered, the chemical solution remaining in the outlet pipe is exposed to air at the outlet of the outlet pipe, allowing the solvent to evaporate into the open space. As a result, the chemical solution is solidified at the outlet of the outlet pipe and tends to clog the outlet pipe.
The rolling and slide bearings used in the in-line pump produce fine particles due to frictional contact between sliding members of the rolling and slide bearings. If the in-line pump is employed in the fabrication semiconductor devices, then such fine particles produced by the rolling and slide bearings contaminate the chemical solution delivered by the in-line pump, resulting in a reduction in the quality of semiconductor wafers. During operation of the in-line pump, the chemical solution finds its way into small gaps that were created in the in-line pump when the in-line pump was assembled of various parts. The chemical solution trapped in those small gaps is liable to be degraded and contaminated with time, and impairs the quality of semiconductor wafers. The chemical solution deposits in the gaps become solidified and stick to the pump parts, making the in-line pump difficult to service for maintenance.